The present invention relates to an electronic key system that permits operation of an in-vehicle device through communication between an electronic key and a vehicle and to an electronic key for such an electronic key system.
An electronic key system for a vehicle includes an electronic key, which serves as a vehicle key. The electronic key transmits an ID code through wireless communication to the vehicle. The vehicle verifies the ID code. Japanese Laid-Open Patent Publication No. 2007-118899 describes one example of such an electronic key system.
In the electronic key system of the publication mentioned above, the vehicle transmits a request signal. The electronic key receives the request signal, measures the strength of the request signal, and automatically sends the measurement (received request signal strength) and the ID code back to the vehicle. Then, the vehicle performs ID verification. A vehicle transmitter transmits the request signal to the interior and exterior of the passenger compartment. A vehicle controller compares the received request signal strength, which is provided from the electronic key, with a predetermined passenger compartment interior threshold and a predetermined passenger compartment exterior threshold. When the received request signal strength is greater than the interior threshold, the vehicle controller determines that the electronic key is located inside the passenger compartment. When the received request signal strength is greater than the exterior threshold but less than or equal to the interior threshold, the vehicle controller determines that the electronic key is located outside the passenger compartment. If the electronic key is located outside the passenger compartment when ID verification is successful, the vehicle controller permits the locking and unlocking of the vehicle doors. If the electronic key is located inside the passenger compartment when ID verification is successful, the vehicle controller permits the starting of the engine.
In the electronic key system of the publication mentioned above, noise may be mixed with the request signal received by the electronic key due to the surrounding environment of the vehicle. Due to such mixed noise, the received request signal strength at the electronic key may differ from the actual received request signal strength. In such a case, the vehicle controller may not be able to correctly determine the location of the electronic key. Further, it is a drawback that the power consumption of the electronic key is increased for noise determination.
It is an object of the present invention to provide an electronic key system and an electronic key that accurately determine the presence of noise in a communication environment and lower power consumption of the electronic key.
One aspect of the present invention is an electronic key system that performs ID verification communication to verify an ID of an electronic key. The ID verification communication is started by transmission of a wireless signal from a vehicle and performed between the vehicle and the electronic key, and the electronic key system determines the location of the electronic key in accordance with a received signal strength of a radio wave used for the ID verification communication. The electronic key system includes a measurement signal transmission circuit that transmits a signal strength measurement signal from the vehicle to the electronic key. A signal strength measurement circuit measures a first signal strength, which is the received signal strength when the signal strength measurement signal from the electronic key is received, and a second signal strength, which is the received signal strength of the radio wave during a vacant time when the electronic key is performing the ID verification communication. A control unit controls operation of the electronic key in accordance with a measurement result of the first signal strength and the second signal strength.
A further aspect of the present invention is an electronic key for use with an electronic key system. The electronic key system performs ID verification communication to verify an ID of the electronic key. The ID verification communication is started by transmission of a signal from a vehicle and performed between the vehicle and the electronic key. The electronic key system determines the location of the electronic key in accordance with a received signal strength of a radio wave used for the ID verification communication. The electronic key includes a receiver that receives the signal strength measurement signal. A signal strength measurement circuit measures a first signal strength, which is the received signal strength when the signal strength measurement signal is received, and a second signal strength, which is the received signal strength of the radio wave in a vacant time during the ID verification communication. A control unit controls operation of the electronic key in accordance with a measurement result of the first signal strength and the second signal strength.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.